Image sensor device with first and second source followers and related methods

ABSTRACT

An image sensor device may include an array of image sensing pixels arranged in rows and columns. Each image sensing pixel may include an image sensing photodiode, a first source follower transistor coupled to the image sensing photodiode, and a switch coupled to the image sensing photodiode. Each image sensor device may include a second source follower transistor coupled to the switch, and a row selection transistor coupled to the first and second source follower transistors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 15/266,345, filed on Sep. 15, 2016, which application is a continuation of U.S. patent application Ser. No. 14/587,401, filed on Dec. 31, 2014, now U.S. Pat. No. 9,570,498, which applications are hereby incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to the field of integrated circuits, and, more particularly, to an image sensor device and related methods.

BACKGROUND

Typically, electronic devices include one or more camera modules for providing enhanced media functionality. For example, the typical electronic device may utilize the camera modules for photo capturing and video teleconferencing. In the typical electronic device with multiple camera modules, the primary camera module has a high pixel density and an adjustable focus lens system, while the secondary camera module is front-facing and has a lower pixel density. Also, the secondary camera module may have a fixed focus lens system.

For example, U.S. Patent Application No. 2009/0057544 to Brodie et al, assigned to the present application's assignee, discloses a camera module for a mobile device. The camera module comprises a lens, a housing carrying the lens, and a lens cap over the lens and housing. The camera module includes a barrel mechanism for adjusting the lens. Each camera module comprises an integrated circuit (IC) image sensor device having a plurality of pixels arranged in an array of rows and columns, a plurality of pixel lines coupled to the plurality of pixels, and readout circuitry coupled to the plurality of pixel lines.

SUMMARY

Generally, an image sensor device may include an array of image sensing pixels arranged in rows and columns. Each image sensing pixel may comprise an image sensing photodiode, a first source follower transistor coupled to the image sensing photodiode, at least one switch coupled to the image sensing photodiode, a second source follower transistor coupled to the at least one switch, and a row selection transistor coupled to the first and second source follower transistors.

The at least one switch may comprise a third transistor having first and second conduction terminals coupled respectively to the image sensing photodiode and to the second source follower transistor. The at least one switch may comprise a fourth transistor coupled between a first reference voltage and the third transistor.

In other embodiments, the at least one switch may comprise third and fourth transistors coupled in series between the image sensing photodiode and a first reference voltage and defining a node therebetween. The second source follower transistor may be coupled to the node.

In some embodiments, the at least one switch may comprise a third transistor coupled to the second source follower transistor and configured to operate based upon a reset signal. Also, each image sensing pixel may comprise a transfer transistor coupled between the image sensing photodiode and the at least one switch. Each image sensing pixel may comprise a reset transistor coupled between a second reference voltage and the transfer transistor. Each image sensing pixel may comprise another switch coupled between a second reference voltage and the second source follower transistor.

Another aspect is directed to an electronic device. The electronic device may include a processor, and an array of image sensing pixels coupled to the processor and arranged in rows and columns. Each image sensing pixel may include an image sensing photodiode, a first source follower transistor coupled to the image sensing photodiode, at least one switch coupled to the image sensing photodiode, a second source follower transistor coupled to the at least one switch, and a row selection transistor coupled to the first and second source follower transistors.

Another aspect is directed to a method for making an image sensor device. The method may include forming an array of image sensing pixels arranged in rows and columns. Each image sensing pixel may include an image sensing photodiode, and a first source follower transistor coupled to the image sensing photodiode. Each image sensing pixel may include at least one switch coupled to the image sensing photodiode, a second source follower transistor coupled to the at least one switch, and a row selection transistor coupled to the first and second source follower transistors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an electronic device, according to the present disclosure;

FIG. 2 is a schematic diagram of an embodiment of an image sensing pixel, according to the present disclosure;

FIG. 3 is a schematic diagram of another embodiment of an image sensing pixel, according to the present disclosure;

FIG. 4 is a schematic diagram of yet another embodiment of an image sensing pixel, according to the present disclosure;

FIG. 5 is a schematic diagram of another embodiment of an image sensing pixel, according to the present disclosure; and

FIG. 6 is a schematic diagram of another embodiment of an image sensing pixel, according to the present disclosure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which several embodiments of the invention are shown. This present disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art. Like numbers refer to like elements throughout, and base 100 reference numerals are used to indicate similar elements in alternative embodiments.

Referring initially to FIGS. 1-2, an electronic device 10 according to the present disclosure is now described. The electronic device 10 illustratively includes a processor ii, and an image sensor device 29 coupled to the processor. The image sensor device 29 illustratively includes an array 12 of image sensing pixels 13 a-13 c arranged in rows and columns. Although only the image sensing pixel 13 a is shown in detail in FIG. 2, it should be appreciated that the other image sensing pixels in the array 29 have similar structure.

Each image sensing pixel 13 a-13 c illustratively includes an image sensing photodiode 20 having an anode coupled to a first reference voltage (e.g. ground) and a cathode, and a transfer transistor 19 having a first conduction terminal coupled to the cathode of the image sensing photodiode, a control terminal coupled to a read command signal node 22, and a second conduction terminal.

Each image sensing pixel 13 a-13 c illustratively includes a sensing node photodiode 21 having an anode coupled to the first reference voltage and a cathode coupled to the second conduction terminal of the transfer transistor 19. Also, each image sensing pixel 13 a-13 c illustratively includes a reset transistor 25 having a control terminal coupled to a reset command signal node 23, a first conduction terminal coupled to a second reference voltage, and a second conduction terminal coupled to the second conduction terminal of the transfer transistor 19 and the cathode of the sensing node photodiode 21.

Moreover, each image sensing pixel 13 a-13 c illustratively includes a first source follower transistor 14 having a control terminal coupled to the second conduction terminal of the transfer transistor 19 and the cathode of the sensing node photodiode 21, thereby coupling it to the image sensing photodiode 20, a first conduction terminal coupled to the second reference voltage, and a second conduction terminal.

Each image sensing pixel 13 a-13 c illustratively includes a switch 16 coupled to the second conduction terminal of the transfer transistor 19 and the cathode of the sensing node photodiode 21, thereby coupling it to the image sensing photodiode 20. Furthermore, each image sensing pixel 13 a-13 c illustratively includes a second source follower transistor 15 having a control terminal coupled to the switch 16, a first conduction terminal, and as second conduction terminal.

Each image sensing pixel 13 a-13 c illustratively includes a row selection transistor 17 having a first conduction terminal coupled to the second conduction terminals of the first and second source follower transistors 14, 15, a control terminal, and a second conduction terminal coupled to a respective column line 24. In this illustrated embodiment, the switch 16 comprises a third transistor 30 having first and second conduction terminals coupled respectively to the image sensing photodiode 20 and to the control terminal of the second source follower transistor 15, and a control terminal coupled to a switch command signal Switch A.

Each image sensing pixel 13 a-13 c illustratively includes a fourth transistor 18 having a control terminal coupled to the same switch command signal Switch A (i.e. transistors 18, 30 have the same conduction state), a first conduction terminal coupled to the second reference voltage, and a second conduction terminal coupled to the first conduction terminal of the second source follower transistor 15.

As will be appreciated, the circuitry of each pixel 13 a-13 c converts the charge generated by the image sensing photodiode 20 into a voltage signal for readout to other circuitry. Advantageously, the second source follower transistor 15 may add extra capacitance to the sensing node of the image sensing photodiode 20. Also, the noise in the voltage signal may be reduced, and the transconductance may be improved. Additionally, the frame rate and image quality of the pixel 13 a-13 c may be increased.

Another aspect is directed to a method for making an image sensor device 29. The method may include forming an array 12 of image sensing pixels 13 a-13 c arranged in rows and columns. Each image sensing pixel 13 a-13 c may include an image sensing photodiode 20, and a first source follower transistor 14 coupled to the image sensing photodiode. Each image sensing pixel may include at least one switch 16 coupled to the image sensing photodiode 20, a second source follower transistor 15 coupled to the at least one switch, and a row selection transistor 17 coupled to the first and second source follower transistors 14, 15.

Referring now additionally to FIG. 3, another embodiment of the image sensing pixel 113 is now described. In this embodiment of the image sensing pixel 113, those elements already discussed above with respect to FIGS. 1-2 are incremented by 100 and most require no further discussion herein. This image sensing pixel 113 has the switch 116 comprising the third transistor 13 o, and the fourth transistor 118. In this embodiment, the fourth transistor 118 has a first conduction terminal coupled to the first reference voltage, a control terminal, and a second conduction terminal coupled to the second conduction terminal of the third transistor 13 o. In this embodiment, the third transistor 13 o, and the fourth transistor 118 have their respective control terminals coupled to first and second switch command signals Switch A, Switch Jr which are inverted to each other (i.e. complementary switch conduction states). Also, the fourth transistor 118 is used to turn off the second source follower transistor 115.

Referring now additionally to FIG. 4, another embodiment of the image sensing pixel 213 is now described. In this embodiment of the image sensing pixel 213, those elements already discussed above with respect to FIGS. 1-2 are incremented by 200 and most require no further discussion herein. This image sensing pixel 213 illustratively includes the switch 216 comprising third and fourth transistors 230, 218 coupled in series between the image sensing photodiode 230 and the first reference voltage and defining a node 231 therebetween, the control terminals being coupled to switch command signal Switch A. The second source follower transistor 215 has its control terminal coupled to the node 231.

Referring now additionally to FIG. 5, another embodiment of the image sensing pixel 313 is now described. In this embodiment of the image sensing pixel 313, those elements already discussed above with respect to FIGS. 1-2 are incremented by 300 and most require no further discussion herein. This image sensing pixel 313 illustratively includes the switch 316 comprising the third transistor 330 coupled to the second source follower transistor 315 and configured to operate based upon a reset signal, i.e. the switch command signal comprises the reset signal from the reset command signal node 323. Also, the image sensing pixel 13 a-13 c illustratively includes another switch 327 coupled between the second reference voltage and the second source follower transistor 315.

In particular, the other switch 327 comprises a transistor having a first conduction terminal coupled to the second reference voltage, a second conduction terminal coupled to the first conduction terminal of the reset transistor 325 and the control terminal of the second source follower transistor 315, and a control terminal coupled to switch reset control signal node 328.

Referring now additionally to FIG. 6, another embodiment of the image sensing pixel 413 is now described. In this embodiment of the image sensing pixel 413, those elements already discussed above with respect to FIGS. 1-2 and 5 are incremented by 400 and most require no further discussion herein. This image sensing pixel 413 differs from the embodiment of FIG. 4 in that the position of the second source follower transistor 415 and the third transistor 430 are swapped.

Many modifications and other embodiments of the present disclosure will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the present disclosure is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims. 

What is claimed is:
 1. An image sensing pixel, comprising: an image sensing photodiode comprising an anode and a cathode, wherein the anode of the image sensing photodiode is coupled to a first reference voltage; a first source follower transistor comprising a control terminal coupled to the cathode of the image sensing photodiode; a switch comprising a first terminal coupled to the control terminal of the first source follower transistor, a second terminal coupled to the first reference voltage, and a node between the first terminal and the second terminal; and a second source follower transistor comprising a control terminal coupled to the node of the switch, wherein the switch comprises a third transistor and a fourth transistor coupled in series with the third transistor, wherein: the third transistor comprises a first conduction terminal forming the first terminal of the switch; a second conduction terminal of the third transistor and a first conduction terminal of the fourth transistor are coupled to form the node of the switch; and a second conduction terminal of the fourth transistor forms the second terminal of the switch.
 2. The image sensing pixel of claim 1, wherein the third transistor and the fourth transistor have different conductivity types.
 3. The image sensing pixel of claim 2, wherein the third transistor and the fourth transistor comprise a p-type transistor and an n-type transistor, respectively.
 4. The image sensing pixel of claim 1, wherein a control terminal of the third transistor and a control terminal of the fourth transistor are coupled to receive a same switch command signal.
 5. The image sensing pixel of claim 1, wherein a first conduction terminal of the first source follower transistor and a first conduction terminal of the second source follower transistor are coupled to a second reference voltage.
 6. The image sensing pixel of claim 1, wherein a second conduction terminal of the first source follower transistor is coupled to a second conduction terminal of the second source follower transistor.
 7. The image sensing pixel of claim 6, further comprising a row selection transistor comprising a first conduction terminal coupled to the second conduction terminal of the second source follower transistor.
 8. The image sensing pixel of claim 7, wherein the row selection transistor further comprises a second conduction terminal coupled to a column line.
 9. The image sensing pixel of claim 1, further comprising a transfer transistor comprising a first conduction terminal coupled to the cathode of the image sensing photodiode, a second conduction terminal coupled to the control terminal of the first source follower transistor, and a control terminal coupled to receive a read command signal.
 10. The image sensing pixel of claim 1, further comprising a reset transistor comprising a first conduction terminal coupled to a second reference voltage, a second conduction terminal coupled to the control terminal of the first source follower transistor, and a control terminal coupled to receive a reset command signal.
 11. The image sensing pixel of claim 1, further comprising a sensing node photodiode comprising a cathode and an anode, wherein the cathode of the sensing node photodiode is coupled to the control terminal of the first source follower transistor, and wherein the anode of the sensing node photodiode is coupled to the first reference voltage.
 12. An electronic device, comprising: a processor; and an array of image sensing pixels coupled to the processor and arranged in rows and columns, each image sensing pixel comprising: an image sensing photodiode comprising an anode and a cathode, wherein the anode of the image sensing photodiode is coupled to a first reference voltage; a first source follower transistor comprising a control terminal coupled to the cathode of the image sensing photodiode; a switch comprising a first terminal coupled to the control terminal of the first source follower transistor, a second terminal coupled to the first reference voltage, and a node between the first terminal and the second terminal; and a second source follower transistor comprising a control terminal coupled to the node of the switch, wherein the switch comprises a third transistor and a fourth transistor coupled in series with the third transistor, wherein: the third transistor is configured to be conducting when the fourth transistor is non-conducting; and the fourth transistor is configured to be non-conducting when the fourth transistor is conducting.
 13. The electronic device of claim 12, wherein: the third transistor comprises a first conduction terminal forming the first terminal of the switch; a second conduction terminal of the third transistor and a first conduction terminal of the fourth transistor are coupled to form the node of the switch; and a second conduction terminal of the fourth transistor forms the second terminal of the switch.
 14. The electronic device of claim 12, wherein a control terminal of the third transistor and a control terminal of the fourth transistor are coupled to receive a same switch command signal.
 15. The electronic device of claim 12, wherein a first conduction terminal of the first source follower transistor and a first conduction terminal of the second source follower transistor are coupled to a second reference voltage.
 16. The electronic device of claim 12, wherein a second conduction terminal of the first source follower transistor is coupled to a second conduction terminal of the second source follower transistor.
 17. The electronic device of claim 16, wherein each image sensing pixel further comprises a row selection transistor comprising a first conduction terminal coupled to the second conduction terminal of the second source follower transistor.
 18. The electronic device of claim 17, wherein the row selection transistor further comprises a second conduction terminal coupled to a column line.
 19. The electronic device of claim 12, wherein each image sensing pixel further comprises a sensing node photodiode comprising a cathode and an anode, wherein the cathode of the sensing node photodiode is coupled to the control terminal of the first source follower transistor, and wherein the anode of the sensing node photodiode is coupled to the first reference voltage.
 20. The electronic device of claim 12, wherein each image sensing pixel further comprises a reset transistor comprising a first conduction terminal coupled to a second reference voltage, a second conduction terminal coupled to the control terminal of the first source follower transistor, and a control terminal coupled to receive a reset command signal. 